My wife wondered what would stop regions from gaining autonomy from the region it's in. So for example Catalonia could become autonomous, but what would stop Barcelona from becoming autonomous from Catalonia? And after that what would stop Girona and Taragona from becoming their own autonomous regions? There's a size limit for what we consider a pizza, and when it's divided you get slices that can't get much smaller or larger either. If you make it much larger or too small, people will identify it as something else. Same will work for governance of small city states or regions, people identify strongly with where they're from. The people who live there don't want to split off from what they identify with because it requires building a new identity. Just like a 15' or a 3/16" slice of pizza would be considered weird. People wouldn't stand for receiving it nor paying for it in kind after ordering it.